In addition, an automatic alignment system was built using the quadrant photodetectors QPD\(_1\)  and QPD\(_2\)  to do differential wavefront sensing in order to maintain the alignment of the injected beam with respect to the cavity Eigenmode [1]}. The actuation is done with the two axes alignment piezo mirrors PZT\(_1\)  and PZT\(_2\)  (see Figure REF ). We were able to realize unity gain frequencies of 170 Hz actuating on PZT\(_2\)  and unity gain frequencies of 15 Hz actuating on PZT\(_1\) .
